Google is always working to create new features that provide additional benefits to our publishers. As part of this objective, Google is currently run a small-scale test of combined Google ad / link units.
This test is taking place on less than 2% of all page views on a random basis, so you may or may not see these units on your pages. During this test, combined units will be served to a small number of regular ad units on publisher pages.
You’ll be paid for all clicks on the Google ads accessed through link unit topics, as well as for clicks on the Google ads that are present in the ad unit. This test is only for a limited time, and AdSense cannot make any commitments as to whether these ad units will be available on a broader basis in the future.